Water-based formulation of h2s/mercaptan scavenger for fluids in oilfield and refinery applications

ABSTRACT

Hydrogen sulfide (H 2 S) and/or mercaptan scavengers are chemicals that remove H 2 S and/or mercaptans from gas, oil and water. Water-based formulations may be made and used employing scavenging compounds having the formulae: 
     
       
         
         
             
             
         
       
     
     wherein each R 1 , R 2 , R 3 , and R 4  are the same or different and are selected from the group consisting of hydrogen, an alkyl, an alkenyl, an aryl, an acyl, a halogen, a hydroxyl, a nitro, an alkyl ester, an aryl ester, an alkyl ether, an aryl ether, a hydroxymethyl, an anhydride group, an amino, and a sulfide. In one non-limiting embodiment the compounds (A) and (B) do not contain nitrogen atoms. Water-based formulations, such as those using a protic solvent with the above compounds, work well as H 2 S scavengers.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional application from U.S. patentapplication Ser. No. 13/172,370 filed Jun. 29, 2011 and issued on ______as U.S. Pat. No. ______, which claims the benefit of U.S. ProvisionalPatent Application Ser. No. 61/360,833 filed Jul. 1, 2010, and is acontinuation-in-part application of U.S. Ser. No. 12/250,679 filed Oct.14, 2008 and issued on Feb. 5, 2013 as U.S. Pat. No. 8,366,914, whichclaims the benefit of U.S. Provisional Patent Application Ser. No.60/980,050 filed Oct. 15, 2007, all of which are incorporated herein intheir entirety by reference.

TECHNICAL FIELD

The present invention relates to methods and compositions for scavengingH₂S and/or mercaptans from fluids, and more particularly relates, in onenon-limiting embodiment, to methods and compositions for scavenging H₂Sand/or mercaptans from fluids having an aqueous phase, a gaseous phaseand/or a hydrocarbon phase using a protic composition comprising aprotic solvent and a scavenger compound.

TECHNICAL BACKGROUND

In the drilling, well completion, production, transport, storage, andprocessing of crude oil and natural gas, including waste waterassociated with crude oil and gas production, and in the storage ofresidual fuel oil, H₂S and mercaptans are often encountered. Thepresence of mercaptans is objectionable because they often react withother hydrocarbons or fuel system components. Another reason that theH₂S and mercaptans are objectionable is that they are often toxic andhighly corrosive. H₂S in aqueous environments can adversely affect theintegrity of pipelines, separators, storage tanks, etc. by corroding thematerials of construction. Even low levels of H₂S in aqueous systems maybe toxic to many living organisms. For instance, a trace amount on theorder of 100 ppm may be fatal to humans. Still another reason thatmercaptans are undesirable is that they have highly noxious odors. Theodors resulting from mercaptans are detectable by the human nose atcomparatively low concentrations and are well known. For example,mercaptans are used to odorize natural gas and used as a repellant byskunks and other animals.

The predominant H₂S scavengers for natural gas and crude oil aremonoethanolamine (MEA) and monomethylamine (MMA) triazines. Thesetriazine compounds, which are amine/aldehyde condensates, containnitrogen and when used in sufficient concentration can cause problemsfor certain refineries. Also, the relatively high dosage rates for thesetriazines, and hence the higher costs, make them less desirable. Inaddition, there are health, safety and environmental (HS&E) concernswith H₂S scavengers that may contain formaldehyde. There have beeninstances where operators have required the use of a non-nitrogencontaining H₂S scavenger. Glyoxal and/or acrolein have been used as aH₂S scavenger in these instances. Glyoxal is corrosive to mild steel.Acrolein is an extremely toxic substance which operators do not like touse.

Metal oxide (e.g. zinc oxide, ferrous oxide, etc.) solutions and causticsolutions (e.g. sodium hydroxide, potassium hydroxide, etc.) have alsobeen used in the past. However, the metal oxide solutions may generateslurries and solids which have disposal issues, and the causticsolutions may be corrosive.

Hydroquinones are known to be useful as mercaptan scavengers. They areused, for example, with a basic solution to catalyze the oxidation ofmercaptans to disulfides to regenerates solvent used for mercaptansexactions from crude oil. Even though hydroquinones have been widelyused, their use has not been trouble free. For example, thehydroquinones require both a basic solution, such as caustic, and oxygento be effective.

U.S. Patent Application Publication No. 2009/0095658 to Yang, et al.(Baker Hughes Incorporated) describes compounds having general formula:

wherein each R₁, R₂, R₃ and R₄ are the same or different and may behydrogen, an alkyl group, an aryl group, a halogen, a nitro group, analkyl or aryl ester, and an alkyl or aryl ether; and other compoundswhere one or two of R₁₋₄ are quaternary ammonium moieties. Thesecompounds can be used as additives for crude oil and hydrocarbons. Thesecompounds are taught as useful to scavenge mercaptans, sulfides,cyanides, and primary or secondary amines; either alone or incombination. In this Publication, these compounds have been formulatedin aprotic solvents such as, but not limited to, aromatic solvents,dichloromethane, chloroform, tetrahydrofuran, N-methyl pyrolidone,dimethyl sulfoxide (DMSO), dimethylformamide (DMF) and the like.

It would be desirable if new H₂S and/or mercaptan scavengers werediscovered which could be implemented in protic solvents, and which didnot necessarily contain nitrogen.

SUMMARY

There is provided in one non-limiting embodiment a method for scavenginghydrogen sulfide and/or mercaptans from a fluid. The fluid may be anaqueous phase, a gaseous phase, a mixture of an aqueous phase and agaseous phase, a mixture of an aqueous phase and a hydrocarbon phase ora mixture of an aqueous phase, a gaseous phase and a hydrocarbon phase.The method involves contacting the fluid with an effective amount of aprotic composition to reduce the amount of hydrogen sulfide and/ormercaptans as compared to an identical method absent the proticcomposition. The protic composition includes: a protic solvent and acompound having a formula selected from the group consisting of:

wherein each R₁, R₂, R₃, and R₄ are the same or different and areselected from the group consisting of hydrogen, an alkyl, an alkenyl, anaryl, an acyl, a halogen, a hydroxyl, a nitro, an alkyl ester, an arylester, an alkyl ether, an aryl ether, a hydroxymethyl, an anhydridegroup, an amino, and a sulfide. Alternatively, none of the R groups arenitro or amino.

There is additionally provided in one non-restrictive version, a proticcomposition for treating fluids containing hydrogen sulfide and/ormercaptans comprising: a protic solvent and a compound having a formulaselected from the group consisting of:

wherein each R₁, R₂, R₃, and R₄ are the same or different and areselected from the group consisting of hydrogen, an alkyl, an alkenyl, anaryl, an acyl, a halogen, a hydroxyl, a nitro, an alkyl ester, an arylester, an alkyl ether, an aryl ether, a hydroxymethyl, an anhydridegroup, an amino, and a sulfide. In one nonlimiting embodiment, none ofthe R groups are nitro or amino.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an uptake test;

FIG. 2 is a graph showing the results of a H₂S uptake test showing massuptake as a function of time; and

FIG. 3 is a graph showing the initial rate of reaction of the ratio ofH₂S mass uptake/active scavenger mass over time comparing a benzoquinonecompound of a method described herein with that of a conventionalamine/aldehyde condensate.

DETAILED DESCRIPTION

It has been discovered that water-based formulations of benzoquinone,specifically para-benzonquinone and ortho-benzoquinone and theirderivatives are effective H₂S and/or mercaptan scavengers for manyfluids, in particular for fluids having an aqueous phase, but also inother systems. The effective scavenging compounds having the generalformulae:

wherein each R₁, R₂, R₃, and R₄ are the same or different and areselected from the group consisting of hydrogen, an alkyl, an alkenyl, anaryl, an acyl, a halogen, a hydroxyl, a nitro, an alkyl ester, an arylester, an alkyl ether, an aryl ether, a hydroxymethyl, an anhydridegroup, an amino, and a sulfide. The number of carbon atoms in the alkylgroup, alkenyl group, aryl group, acyl group, alkyl ester group, arylester group, alkyl ether group, aryl ether, or anhydride group may rangefrom 1 independently to 10; alternatively from 1 independently to 5. Bythe term “independently” as used herein with respect to ranges is meantthat any lower threshold may be used together with any upper thresholdto provide a valid alternative range. By a nitro group is meant —NO₂.

In one non-limiting embodiment, R_(n) is not a nitro group or an aminogroup to avoid the compound containing nitrogen. It has beensurprisingly found that the above mentioned compounds have worked as H₂Sscavengers when formulated in protic solvents such as water, methanoland ethanol, and that good results are obtained.

Aqueous solutions of both ortho- and para-quinones (formulae (B) and(A)) may be used to remove H₂S and/or mercaptans from natural gas or oilby a method involving introducing an aqueous solution of thebenzoquinone into the gas or oil. In alkaline solutions (defined in onenon-limiting embodiment as having a pH above 10), the ortho- andpara-quinines, depending upon prevalent redox conditions (i.e. pH) maybe present in fully reduced, intermediate or fully oxidized states asshown in formulae (I)-(V) below for para-quinone:

where R is R₁, R₂, R₃ and/or R₄ as previously defined. When both fullyreduced (I and IV) and oxidized (V) forms of a quinine are present inalkaline solution they can exchange electrons to form semi-quinoneradicals (II and III). The semiquinone and fully oxidized quinone reactwith hydrogen sulfide to form an addition reaction product via an α-βconjugated system. This reaction product does not contain elementalsulfur whose presence in oil and/or gas systems is considereddetrimental to the production system's integrity.

Unlike the addition reaction of H₂S with semi-quinone and fully oxidizedquinine in alkaline solutions, the reaction with quinone (V) innonaqueous solutions (defined in one non-limiting embodiment as a pH ofless than 8) occurs with the formation of elemental sulfur. (Forinstance, see U.S. Pat. Nos. 4,592,905 and 5,180,572 incorporated hereinby reference in their entirety.)

In one non-limiting embodiment, the protic solvent may be water;alternatively the protic solvent may be alcohols, glycols and mixturesthereof alone or without water. Suitable alcohols include methanol andethanol. Other possible solvents can be isopropyl alcohol, n-propanoland n-butanol (n-butyl alcohol). Dimethyl formamide may also be used asan aprotic solvent.

The amount of the component (A) or (B), such as benzoquinone, in theprotic composition may range from about 5 to about 40 mass %,alternatively from about 10 independently to about 30 mass %.

In one non-limiting embodiment the protic composition containing thecompound has a pH of greater than 9; alternatively the composition has apH of from about 11 to about 13.

To accomplish the rise in pH, a base may be added. Suitable basesinclude, but are not necessarily limited to, sodium hydroxide, potassiumhydroxide and combinations thereof. The base is present in aconcentration effective to give the composition a pH of greater than 9,in another non-limiting embodiment, a pH of from about 11 to about 13.There is some indication that acceptable results may be achieved with apH of about 12.

The protic formulations or compositions may also contain a surfactant,which may act as a dispersant. Suitable surfactants that may be usedinclude, but are not necessarily limited to, nonyl phenol ethoxylates.

It has been discovered that water-based formulations of these compoundsact as hydrogen sulfide scavengers when the hydrogen sulfide is presentin the aqueous phase, the gaseous phase and/or a hydrocarbon phase. Themethod and compositions described herein may be used to remove H₂Sand/or mercaptans from aqueous systems including, but not necessarilylimited hydrogen sulfide from, water injection systems, produced waterfrom an oilfield, hydrogen sulfide present in mixed production streamsand the like. These methods and compositions may also be used to removehydrogen sulfide present in natural gas produced from natural gas wells.It is expected that the methods and compositions may be used to removehydrogen sulfide in crude oil. These methods and compositions may alsobe used to remove hydrogen sulfide from brines containing hydrogensulfide. These methods and compositions may provide a non-nitrogen-basedH₂S and/or mercaptan scavenger.

The methods described herein may involve scavenging H₂S and/ormercaptans from a fluid including an aqueous phase, a hydrocarbon phaseand mixtures thereof. In this embodiment, the compound may be present inthe protic or aqueous composition in a concentration from about 50independently to about 1000 ppm; alternatively from about 50 ppmindependently to about 200 ppm.

In one non-limiting embodiment the amount of the protic composition usedin the fluid may range from about 50 wt % independently to about 99 wt%, alternatively from about 60 wt % independently to about 85 wt %.Alternatively, the dosage range is from about 10 independently to about300 ppm of the active compound per ppm of the H₂S and/or the mercaptan;alternatively from about 10 independently to about 20 ppm of the activecompound per ppm of the H₂S and/or the mercaptan. In one non-limitingembodiment the method is practiced in a refinery.

When the method scavenges H₂S and/or mercaptans from a gaseous phase,the method may be practiced by contacting the gaseous phase withdroplets of the composition, in one non-limiting embodiment a mist,and/or passing the gaseous phase through the composition, such asthrough a liquid phase of the protic composition, such as by bubblingthrough a tower. With respect to removing H₂S and/or mercaptans from agaseous phase, the compound is present in the protic composition in aconcentration of at least 50 vol %, alternatively at least 60 vol %,alternatively at least 70 vol %, alternatively at least 80 vol %,alternatively at least 90 vol %, and alternatively at least 95 vol %.

It has also been discovered that compounds having the general formulae(A) and (B) may be effective to scavenge H₂S in gaseous systems, whichformulae include benzoquinones (C₆H₄O₂) and their derivatives.Particular useful formulations include, but are not necessarily limitedto 20 ppm per ppm H₂S of benzoquinone in dimethylformamide and 17 ppmbenzoquinone in diglyme. However, these are aprotic solvents.

It has also been discovered that the compositions and methods herein maybe used to scavenge H₂S and/or mercaptans in gaseous systems. Themethods and compositions are found to have higher kinetics thanconventional amine/aldehyde condensates. FIG. 3 presents a graphdemonstrating that the initial rate of reaction between a compound asdescribed herein (15 wt % para-benzoquinone, 4.5 wt % KOH and 80.5 wt %water) and H₂S is about two times faster than that of a conventionalamine/aldehyde condensate. In addition, the compositions discussedherein generally provide higher H₂S-scavenging capacities thantraditional amine/aldehyde condensate.

Because of this fast reaction rate, the methods and compositionsdescribed herein have an advantage to scavenge H₂S and/or mercaptanswhere contact time is limited. In one non-restrictive example, onoffshore platforms where space is limited, and hence there are shortcontact times between scavengers and H₂S, often operators have toover-inject chemicals in order to reduce H₂S levels to acceptablevalues. However, with the methods and compositions described herein, itis expected that much shorter contact times will be needed to reduce H₂Sto acceptable levels. As a result, operators do not have to build anduse extra long flow loops in order to provide the extra distance (andextra contact time) that is necessary to scavenge H₂S before salespoints.

Further details about the compounds and their methods of use may befound with reference to U.S. Patent Application Publication No.2009/0095658 incorporated herein in its entirety by reference.

The invention will now be illustrated with respect to certain exampleswhich are not intended to limit the invention in any way but simply tofurther illustrate it in certain specific embodiments.

Example 1

A formulation that contains 15% para-benzoquinone, 4.5% potassiumhydroxide, and 80.5% water was made. These amounts are mass %. Uptaketests were conducted with this formulation. A schematic diagram of theuptake test is shown in FIG. 1. This test was also used to generate thedata of FIG. 3. The pH of this formulation was about 10.

The liquid used in the tests was Aromatic 100. Aromatic 100 is acommonly used liquid solvent identified with CAS 64742-95-6. In thetests conducted using the protic solvent based formulation, 5.05 gms ofthe formulation were put into 44.96 gm of Aromatic 100. The results areshown in FIG. 2.

It can be seen that tests with just Aromatic 100 resulted in a massuptake of only about 0.25 gm whereas the tests with the formulation inAromatic 100 resulted in a mass gain of about 0.96 gm with theformulation in aromatic 100 when it was not stirred and a mass gain ofabout 1.14 g for the formulation in aromatic 100 that was stirred. Theformulation did contain 0.228 gms of potassium hydroxide. In order toform potassium sulfide, this would react with 0.07 gms of hydrogensulfide. Here mass gains of 0.64 gm of hydrogen sulfide were obtainedfor the unstirred case and 0.82 gm of hydrogen sulfide was obtained forthe stirred case which can only be the result of the protic solventbased formulation.

In the foregoing specification, the invention has been described withreference to specific embodiments thereof, and has been demonstrated aseffective in providing methods and compositions for scavenging H₂Sand/or mercaptans from aqueous fluids, hydrocarbon fluids, gaseousphases and combinations thereof. However, it will be evident thatvarious modifications and changes can be made thereto without departingfrom the broader spirit or scope of the invention as set forth in theappended claims. Accordingly, the specification is to be regarded in anillustrative rather than a restrictive sense. For example, specificprotic solvents and hydroquinone compounds and derivatives thereoffalling within the claimed parameters, but not specifically identifiedor tried in a particular composition or method, are expected to bewithin the scope of this invention.

The words “comprising” and “comprises” as used throughout the claims isinterpreted “including but not limited to”.

The present invention may suitably comprise, consist or consistessentially of the elements disclosed and may be practiced in theabsence of an element not disclosed. For instance, the proticcomposition may consist of or consist essentially of the protic solventand the compound of formulae (A) and (B) as the solvent and compound aredefined in the claims. In another nonlimiting instance, the method forscavenging hydrogen sulfide and/or mercaptans from a fluid including,but not necessarily limited to, an aqueous phase, a gaseous phase, amixture of an aqueous phase and a gaseous phase, a mixture of an aqueousphase and a hydrocarbon phase and a mixture of an aqueous phase, agaseous phase and a hydrocarbon phase may consist of or consistessentially of contacting the fluid with an effective amount of a proticcomposition to reduce the amount of hydrogen sulfide and/or mercaptansas compared to an identical method absent the protic composition, wherethe protic composition consists of or consists essentially of a proticsolvent and a compound having a formula (A) and/or (B) as described inthe claims.

What is claimed is:
 1. A protic composition for treating fluidscontaining hydrogen sulfide comprising: a protic solvent; optionally abase selected from the group consisting of sodium hydroxide, potassiumhydroxide and combinations thereof; and a non-nitrogen-based compoundhaving a formula selected from the group consisting of:

wherein each R₁, R₂, R₃, and R₄ are the same or different and areselected from the group consisting of hydrogen, an alkyl, an alkenyl, anaryl, an acyl, a halogen, a hydroxyl, an alkyl ester, an aryl ester, analkyl ether, an aryl ether, a hydroxymethyl, an anhydride, and asulfide, where the protic composition reduces the amount of hydrogensulfide in the fluid as compared to an identical method absent theprotic composition, where the fluid is selected from the groupconsisting of: an aqueous phase, a gaseous phase, a mixture of anaqueous phase and a gaseous phase, a mixture of an aqueous phase and ahydrocarbon phase, and a mixture of an aqueous phase, a gaseous phaseand a hydrocarbon phase.
 2. The protic composition of claim 1 having apH of greater than
 9. 3. The protic composition of claim 1 having a pHof from about 11 to about
 13. 4. The protic composition of claim 1comprising a base selected from the group consisting of sodiumhydroxide, potassium hydroxide and combinations thereof, the base beingpresent at a concentration effective to give the composition a pH ofgreater than
 9. 5. The protic composition of claim 1 where the proticsolvent is selected from the group consisting of water, alcohols,glycols, and combinations thereof.
 6. The protic composition of claim 1where the non-nitrogen-based compound is present in the proticcomposition at a concentration of from about 50 to about 1000 ppm.
 7. Aprotic composition for treating fluids containing hydrogen sulfidecomprising: a protic solvent selected from the group consisting ofwater, alcohols, glycols, and combinations thereof; optionally a baseselected from the group consisting of sodium hydroxide, potassiumhydroxide and combinations thereof; and from about 50 to about 1000 ppmpresent in the protic composition of a non-nitrogen-based compoundhaving a formula selected from the group consisting of:

wherein each R₁, R₂, R₃, and R₄ are the same or different and areselected from the group consisting of hydrogen, an alkyl, an alkenyl, anaryl, an acyl, a halogen, a hydroxyl, an alkyl ester, an aryl ester, analkyl ether, an aryl ether, a hydroxymethyl, an anhydride, and asulfide, where the protic composition reduces the amount of hydrogensulfide in the fluid as compared to an identical method absent theprotic composition, where the fluid is selected from the groupconsisting of: an aqueous phase, a gaseous phase, a mixture of anaqueous phase and a gaseous phase, a mixture of an aqueous phase and ahydrocarbon phase, and a mixture of an aqueous phase, a gaseous phaseand a hydrocarbon phase; and where the protic composition has a pH ofgreater than
 9. 8. The protic composition of claim 7 having a pH of fromabout 11 to about
 13. 9. The protic composition of claim 7 comprising abase selected from the group consisting of sodium hydroxide, potassiumhydroxide and combinations thereof, the base being present at aconcentration effective to give the composition a pH of greater than 9.10. A protic composition for treating fluids containing hydrogen sulfidecomprising: a protic solvent; a base selected from the group consistingof sodium hydroxide, potassium hydroxide and combinations thereof; and anon-nitrogen-based compound having a formula selected from the groupconsisting of:

wherein each R₁, R₂, R₃, and R₄ are the same or different and areselected from the group consisting of hydrogen, an alkyl, an alkenyl, anaryl, an acyl, a halogen, a hydroxyl, an alkyl ester, an aryl ester, analkyl ether, an aryl ether, a hydroxymethyl, an anhydride, and asulfide, where the protic composition reduces the amount of hydrogensulfide in the fluid as compared to an identical method absent theprotic composition, where the fluid is selected from the groupconsisting of: an aqueous phase, a gaseous phase, a mixture of anaqueous phase and a gaseous phase, a mixture of an aqueous phase and ahydrocarbon phase, and a mixture of an aqueous phase, a gaseous phaseand a hydrocarbon phase; and the protic composition having a pH of fromabout 11 to about
 13. 11. The protic composition of claim 10 comprisinga base at a concentration effective to give the composition a pH ofgreater than
 9. 12. The protic composition of claim 10 where the proticsolvent is selected from the group consisting of water, alcohols,glycols, and combinations thereof.
 13. The protic composition of claim10 where the non-nitrogen-based compound is present in the proticcomposition at a concentration of from about 50 to about 1000 ppm.